1. Field of the Invention
Present invention relates to a low hydrogen-content silicon crystal with few micro-defects including supersaturating oxygen which has been generated in the device manufacturing process, as well as relates to its manufacturing methods.
2. Description of the Related Arts
Silicon crystals used to manufacture an electric or a minute device, for instance, a substrate crystal, are usually manufactured from the Czochralski method which uses a quartz crucible.
The silicon crystal manufactured from the Czochralski method, referred to hereinafter as Cz silicon crystal, includes supersaturated oxygen. Supersaturated oxygen generates defects with oxygen during an annealing process in manufacturing the semiconductor device. As a result, the characteristic of the semiconductor device is deteriorated and its manufacturing yield is decreased. Therefore, a Cz silicon crystal which includes oxygen but does not cause the defect in the annealing process has been requested.
It is known that precipitation of the supersaturated oxygen in the silicon crystal is influenced by carbon, nitrogen and intrinsic point defects density. However, relation between other impurities and the oxygen precipitation has been hardly known.
It was reported recently by the inventor of the present invention on the 1993 Solid State Devices and Materials Conference p.1014, and the Journal of Applied Physics, vol. 74, (1993) p.913-916, that a small amount of hydrogen is included in the Cz silicon crystal, and the hydrogen supersaturated in the silicon crystal easily forms a aggregation resulting in generation of lattice defects. This fact suggests that there is the possibility that the precipitation of the supersaturated oxygen in the silicon crystal is also influenced by the small amount of hydrogen included in the crystal. Therefore, the necessity for clarifying the relation between the hydrogen density in the crystal and the oxygen precipitation has been recognized.
However, because the hydrogen concentration in the Cz silicon crystal is extremely low, its quantitative measurement is difficult. For instance, an infrared absorption method known for its high sensitivity measurement as well as a secondary ion mass spectroscopy (SIMS) have been used for the measurement of the hydrogen concentration in the silicon crystal. However, the hydrogen concentration in the as-grown Cz silicon crystal has not been measured yet due to the limit of the measurement sensitivity because the achievement of the measurement with these methods were for the crystal in which an intentionally large amount of hydrogen was doped.
Thus, because the low concentration of hydrogen in the Cz silicon crystal could not be quantitatively measured by the prior arts, it was impossible to quantitatively examine the relation between the hydrogen concentration in the Cz silicon crystal and the formation of the lattice defect. Therefore, it has still been uncertain whether such an extremely low concentration of hydrogen, such as the hydrogen in the Cz silicon crystal actually used for manufacturing semiconductor devices, influences the generation of the lattice defect during the annealing process.